This application is based on and claims priority to Japanese Patent Application No. 11-067654, filed Mar. 15, 1999, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
The present invention relates to fuel injected engines and, in particular, to an improved combustion chamber design and injection timing strategy for a fuel injected engine.
2. Description of the Related Art
There are two general categories of fuel supply systems for internal combustion engines. One type of fuel system utilizes a carburetor, which delivers a generally constant air/fuel ratio during a given intake cycle. The other type of fuel system utilizes fuel injection, which delivers a finite amount of fuel to the engine generally once per combustion cycle. Typically, in a fuel injected engine, the fuel is either injected into the induction system or injected directly into the combustion chamber. The later method is generally referred to as direct fuel injection.
The current trend in the industry is to use direct fuel injection to improve performance, emissions and fuel economy. One of the advantages of direct fuel injection is that the charge in the combustion chamber can be stratified. That is, the fuel can be directed towards the spark plug such that the fuel/air mixture is rich around the spark plug gap. Accordingly, the engine can be run at an overall leaner fuel/air ratio. This reduces the amount of unburned hydrocarbons in the exhaust and increases fuel economy.
To obtain more effective stratification in the combustion chamber, the piston head typically includes a bowl that is offset towards one side of the combustion chamber. This arrangement encourages a xe2x80x9ctumble flowxe2x80x9d of fuel and air from the bowl into the area where the spark gap exists. Such an arrangement enhances the rich conditions around the ignition area.
There are, however, several problems associated with conventional direct fuel injected engines. For example, at high-speed and high-load conditions, a large volume of gasoline must be injected into the combustion chamber. Accordingly, the injection of fuel must be advanced (i.e., with respect to the spark plug firing) so that the fuel has sufficient time to vaporize and mix with the air. However, such advanced fuel injection tends to produce smoke in the exhaust discharge.
There are typically two types of smoke in the exhaust discharge. White exhaust smoke comprises tiny droplets of liquid that are made up of mainly fuel and water. White exhaust smoke typically occurs during cold starts and/or when there is poor vaporization of the liquid fuel. These fuel droplets remain unburnt after the combustion process and are discharged through the exhaust. Black exhaust smoke is formed when fuel is subjected to rich conditions. During such conditions, the hydrogen molecules of the fuel are preferentially oxidized. The remaining carbon atoms are difficult to burn and thus remain unburnt after the combustion and are discharged as particulates with the discharge gases.
Accordingly, there is a need for an improved fuel injected engine that reduces the amount of exhaust smoke at high engine speeds and loads.
One aspect of the present invention includes the recognition that the exhaust smoke, which is typically associated with direct fuel injection at high speeds/loads, is caused in part by high fuel densities. High fuel densities in the combustion chamber can produce black exhaust smoke as hydrogen molecules of the fuel are oxidized preferentially. High fuel densities also inhibit the vaporization of the fuel, which can produce white exhaust smoke. Poor fuel vaporization can also impair cooling of the intake air, which can lead to engine knock. These problems are particularly present when fuel is injected into the combustion chamber at a crankangle of 10-40 degrees past top-dead center during the start of the intake stroke. Accordingly, it is desirable to start fuel injection after this range of crankangles that correspond to a xe2x80x9cexhaust smoke zonexe2x80x9d.
At high speeds/loads, however, a large volume of fuel must be injected into the combustion chamber. Accordingly, if fuel injection is delayed so that fuel injection starts after the exhaust smoke zone (e.g., approximately 40 degrees past top-dead center), then the fuel injection must continue until the intake stroke is almost complete. In such an arrangement, much of the fuel will be injected after the intake cam achieves its maximum lift. This is undesirable because the fuel injected after the intake cam achieves its maximum lift is not mixed as effectively. Accordingly, the quality of the combustion is reduced thereby reducing engine torque.
Accordingly, one aspect of the of the present invention involves an internal combustion engine that comprises an engine body assembly that defines at least one cylinder closed at one end, The engine further comprises at least one piston that reciprocates within the cylinder and at least one combustion chamber formed within the engine body assembly by the cylinder, the closed end of the cylinder and the piston. The piston has a head that faces the closed end of the cylinder. The piston is coupled to an output shaft such that movement of the reciprocating movement of the piston causes the output shaft to rotate. A fuel injector is arranged to supply fuel to the combustion chamber. The fuel injector includes an actuator to control a flow of fuel through the fuel injector. A fuel control system is coupled to the actuator and is configured to control the actuator so as to not inject fuel into the combustion chamber when the output shaft is within a prohibited shaft angle range that is located past a top-dead-center position.
Another aspect of the of the present invention involves an internal combustion engine that operates on a four-stroke cycle. The engine comprises an engine body assembly defining at least one cylinder closed at one end, a piston reciprocating within the cylinder, and at least one combustion chamber formed within the engine body assembly by the cylinder, the closed end of the cylinder and the piston. The piston has a head that faces at least one intake port and at least one exhaust port. The piston is coupled to an output shaft such that movement of the reciprocating movement of the piston causes the output shaft to rotate. An intake valve opens and closes during each cycle to regulate the flow of intake are into the combustion chamber. A fuel injector supplies fuel to the combustion chamber. The fuel injector includes an actuator to control a flow of fuel through the fuel injector. A fuel control system is coupled to the actuator and configured to inject fuel into the combustion chamber in at least a first stage and a second stage during each cycle. The first and second stages are separated by a rest period. The first and second stages are completed before the intake valve closes during each cycle.
Yet, another aspect of the present invention involve an internal combustion engine that operates on a four-stroke cycle. The engine comprises an engine body assembly defining at least one cylinder closed at one end, at least one piston reciprocating within the cylinder, and at least one combustion chamber formed within the engine body assembly by the cylinder, the closed end of the cylinder and the piston. The piston has a head that faces the closed end of the cylinder. The piston is coupled to an output shaft such that movement of the reciprocating movement of the piston causes the output shaft to rotate. A fuel injector supplies fuel to the combustion chamber. The fuel injector includes an actuator to control a flow of fuel through the fuel injector. A fuel control system is coupled to the actuator and configured to inject fuel into the combustion chamber before the piston reaches a top-dead-center position of an intake stroke.
Another aspect of the invention involves a method for operating an internal combustion. The method includes reciprocating a piston within a cylinder of the engine through power, exhaust, intake and compression strokes of repeating combustion cycles. The method also includes injecting fuel into a combustion chamber, which is formed within the cylinder, during a first injection stage during each cycle. The method further includes ceasing fuel injection during a rest period occurring within the intake stroke and injecting fuel into the combustion chamber during a second stage after the rest period.
All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed.